Implantable medical devices for the repair of vascular defects, including for example vascular aneurysms, are well known in the art. A common device for treatment of such a medical condition is a stent-graft.
Medical devices of this type are typically deployed endoluminally through a vein or artery adjacent a surface of a patient, aortic devices, for example, being commonly fed through the femoral artery. A generally accepted method of deployment involves the location of a guide wire along the path to be followed by the introducer assembly, up to the site in the vasculature to be treated. Once the guide wire is in place, a series of catheters is advanced along the guide wire, finally with the introduction of a catheter assembly which carries the stent or stent-graft to be fitted. The catheters have sufficient trackability to follow the guide wire along the curves and turns of the patient's vasculature and some can also curve sufficiently so as to be able to fit a stent-graft, for example, into a highly curved vessel such as the aortic arch.
Even though such a procedure is possible into the aortic arch, it is mired in difficulties as a result of the tight curvature of the aorta in this location. One such difficulty arises in connection with the proximal end of the stent-graft, which is liable to be incorrectly fitted such that it incompletely seals around the inner wall of the aorta as a result of the curvature imparted to the stent-graft. This can lead to leakage of blood around the outside of the stent-graft and thus a less than effective treatment. Furthermore, as a result of the non-optimal placement of the stent-graft using known procedures, it is necessary to have a reasonable length of healthy vascular wall in order to provide a seal around the proximal end of the stent-graft. This limits the application of such stent-grafts, in particular for the treatment of aneurysms close to a branch vessel and to conditions where there is at least a certain length of healthy vessel wall tissue, thus making the procedure not available to treat a reasonable proportion of medical cases.
In addition, in some instances at least, a part of the proximal end of the stent-graft can remain loosely located in the vessel, leading to premature fatigue failure as well as thrombus effects.
Attempts have been made to resolve these difficulties. For instance, in the applicant's U.S. Pat. No. 6,974,471, mechanisms are described for imparting a curvature to the stent-graft at the moment of its deployment.
Another example, disclosed in US-2006/155366, applies a curve to the introducer assembly in order to impart a curvature to the stent graft in order to place the latter in a curved lumen.
The deployment of stent-grafts and other devices, particularly in the aortic arch, in lumens having short necks of healthy vascular wall and other difficult pathologies also requires very precise placement of the device to ensure a good coupling to healthy tissue and in particular a coupling which has longevity and which provides a fluid-tight seal with the vessel wall. Prior art systems do allow for a certain amount of coarse re-positioning of the device. However, if the device is not fitted precisely in the correct location, the procedure may need to be repeated, for example by withdrawing the device back into its delivery introducer (where this is possible) and starting the deployment operation afresh. Repeating the procedure increases operating time, trauma to the patient and still does not guarantee a successful outcome. In some instances, it is necessary to abort the procedure.
Prior art introducer systems include wire tie elements able to pull the proximal end of the stent graft in the direction of the introducer. This does not, however, always provide a mechanism for ensuring correct positioning of the proximal end of the stent graft in a lumen, particularly in cases where the lumen is particularly curved.
Problems can also arise with the correct placement and orientation of a stent graft in other lumens or regions of the aorta of a patient and in order to ensure correct placement stent grafts are often provided with a stent ring which extends beyond the end of the graft material, often being called a bare stent. Such a bare stent typically plays no part in closing off blood supply to a lumen or part thereof, as does a graft covered stent, and normally only serves to support the end of the graft material correctly in the lumen.
While such bare stents can achieve the intended function efficiently, they can be the cause of other problems. For example, they require a length of suitable lumen against which to press. They can also induce stenosis or restenosis in the location in which they are fitted.